The three biological gaps and hyperoxaluria in ethylene glycol poisoning: case presentation and review.

Ethylene glycol is a toxic alcohol which may induce significant toxicity when ingested accidentally or intentionally. The main clinical complications of EG poisoning include central nervous system depression, cardiorespiratory instability and renal failure, which may be lethal if improperly treated. Although the demonstration of high plasma levels of ethylene glycol confirms the intoxication, such measurements are generally not obtained in the acute setting and can be misleading due to the rapid metabolism of EG. This implies the need for alternative, indirect, diagnostic methods, which reflect the metabolic fate of EG. These include an early and transient osmolar gap, followed by an anion gap metabolic acidosis and hyperoxaluria. Another frequent finding is a lactate gap between various methods of lactate measurements. An appropriate knowledge of these laboratory findings is essential for the diagnosis of EG poisoning, and for the initiation of antidote therapy (fomepizole) and hemodialysis in selected cases. These features are illustrated by the presentation of a prototypical case of EG poisoning, in which an incomplete diagnostic workup on hospital admission resulted in an unnecessary laparotomy and a significant delay in the management of the intoxication.

Delayed administration of N-acetylcysteine blunts recovery after an acetaminophen overdose unlike 4-methylpyrazole.

N-acetylcysteine (NAC) is the only clinically approved antidote against acetaminophen (APAP) hepatotoxicity. Despite its efficacy in patients treated early after APAP overdose, NAC has been implicated in impairing liver recovery in mice. More recently, 4-methylpyrazole (4MP, Fomepizole) emerged as a potential antidote in the mouse APAP hepatotoxicity model. The objective of this manuscript was to verify the detrimental effect of NAC and its potential mechanism and assess whether 4MP has the same liability. C57BL/6J mice were treated with 300 mg/kg APAP; 9 h after APAP and every 12 h after that, the animals received either 100 mg/kg NAC or 184.5 mg/kg 4MP. At 24 or 48 h after APAP, parameters of liver injury, mitochondrial biogenesis and cell proliferation were evaluated. Delayed NAC treatment had no effect on APAP-induced liver injury at 24 h but reduced the decline of plasma ALT activities and prevented the shrinkage of the areas of necrosis at 48 h. This effect correlated with down-regulation of key activators of mitochondrial biogenesis (AMPK, PGC-1α, Nrf1/2, TFAM) and reduced expression of Tom 20 (mitochondrial mass) and PCNA (cell proliferation). In contrast, 4MP attenuated liver injury at 24 h and promoted recovery at 48 h, which correlated with enhanced mitochondrial biogenesis and hepatocyte proliferation. In human hepatocytes, 4MP demonstrated higher efficacy in preventing cell death compared to NAC when treated at 18 h after APAP. Thus, due to the wider treatment window and lack of detrimental effects on recovery, it appears that at least in preclinical models, 4MP is superior to NAC as an antidote against APAP overdose.

Single versus continued dosing of fomepizole during hemodialysis in ethylene glycol toxicity.

BACKGROUND: In cases of ethylene glycol (EG) toxicity requiring hemodialysis (HD), fomepizole is dosed every four hours. HD efficiently clears EG and its toxic metabolites, and it's unclear if multiple doses (MD) of fomepizole improve patient outcomes or whether a single dose (SD) prior to initiation of HD is sufficient. METHODS: We reviewed cases of EG toxicity at a toxicology referral center from 2008 to 2018. Patients treated with HD with EG levels greater than 20 mg/dL were included. Duration of dialysis, creatinine at discharge, hospital length of stay (LOS), and complications were analyzed. We compared patients who received a single dose of fomepizole prior to HD to those who received continued dosing during and after HD. RESULTS: Twenty-five patient encounters were identified (MD: 20; SD: 5). Initial bicarbonate (11 [SD] vs. 9 mg/dL [MD]) and pH (7.1 vs. 7.1) were similar between the groups; however, there was a trend toward a greater proportion of patients with renal dysfunction in the MD group: 11 (55%) vs. 1 (20%). HD was initiated a median interval of 5.2 h [SD] vs. 5.7 h [MD] after a dose of fomepizole. There was one death in the MD group and none in the SD group. Median creatinine on the day of discharge was 0.7 mg/dL (IQR: 0.57-3.8) in the SD group and 2.0 mg/dL (0.90-7.0) in the MD group. LOS was similar (5.8 days [95% CI 3.6-8.0] vs. 7.6 days [5.3-9.9]) (p = .61). CONCLUSION: Patients with moderately severe EG toxicity (acidosis and no initial renal dysfunction) treated with a single dose of fomepizole prior to HD had similar outcomes to those receiving continued dosing of fomepizole during or after HD. This raises the possibility that a single dose of fomepizole may be sufficient if HD is initiated quickly.

Novel strategies for the treatment of acetaminophen hepatotoxicity.

INTRODUCTION: Acetaminophen (APAP) hepatotoxicity is the leading cause of acute liver failure in the western world. Despite extensive investigations into the mechanisms of cell death, only a single antidote, N-acetylcysteine, is in clinical use. However, there have recently been more efforts made to translate mechanistic insight into identification of therapeutic targets and potential new drugs for this indication. AREAS COVERED: After a short review of the key events in the pathophysiology of APAP-induced liver injury and recovery, the pros and cons of targeting individual steps in the pathophysiology as therapeutic targets are discussed. While the re-purposed drug fomepizole (4-methylpyrazole) and the new entity calmangafodipir are most advanced based on the understanding of their mechanism of action, several herbal medicine extracts and their individual components are also considered. EXPERT OPINION: Fomepizole (4-methylpyrazole) is safe and has shown efficacy in preclinical models, human hepatocytes and in volunteers against APAP overdose. The safety of calmangafodipir in APAP overdose patients was shown but it lacks solid preclinical efficacy studies. Both drugs require a controlled phase III trial to achieve regulatory approval. All studies of herbal medicine extracts and components suffer from poor experimental design, which questions their clinical utility at this point.

Health-related quality of life determinants in survivors of a mass methanol poisoning outbreak: six-year prospective cohort study.

Purpose: The effect of acute methanol poisoning on the follow-up quality of life of survivors in mass poisoning outbreaks is not known. The objective of this is to study the impact of visual and central nervous system (CNS) sequelae of methanol poisoning on long-term health-related quality of life (QoL) of survivors, its clinical determinants, and dynamics.Materials and methods: A total of 54 patients with confirmed methanol poisoning (mean age 46.7 ± 13.4 years, 9 females) were examined consequently three times within six-year prospective cohort study and compared to 23 controls with the history of chronic alcohol abuse. The following tests were performed: SF-36 QoL questionnaire, visual evoked potentials (VEP) of optic nerve, ocular examination with retinal nerve fiber layer (RNFL) thickness measurement, brain magnetic resonance imaging (MRI), and biochemical and toxicological tests.Results: Acute methanol poisoning led to significant decrease in physical component summary (PCS) compared to PCS of age-adjusted controls (mean score with SD 46.8 ± 11.0 versus 52.3 ± 9.4 points; p = .003). In 17/40 (42.5%) patients with three rounds of examination, signs of severe disability (≤30 points in at least one score) were present six years after discharge, with negative dynamics of PCS score during the observation period. The patients with abnormal RNFL thickness had lower PCS (mean difference 10.5 points; 95%CI 3.5-17.5, p = .004) and mental component summary score (9.5 points; 95%CI 1.9-17.1, p = .015) compared to the patients with normal RNFL. Signs of physical and mental adaptation to long-term visual sequelae were registered with gradual reduction of difference in most of physical and mental components scores compared to the patients with normal RNFL during six years of observation. Signs of hemorrhagic brain lesions were associated with permanent decrease of PCS score (mean difference 7.4 points; 95%CI 0.6-14.0; p = .033), bodily pain (8.7 points; 95%CI 1.6-17.6; p = .018), and social functioning (8.2 points; 95%CI 3.0-17.4; p = .005) six years after discharge. No effect of type of antidote (fomepizole versus ethanol) and extracorporeal enhanced elimination modality (intermittent hemodialysis versus continuous renal replacement therapy) applied in hospital on long-term QoL was found (all p > .05).Conclusion: Acute methanol poisoning was associated with a significant decrease of health-related quality of life of survivors persisting for at least six years after discharge. The more pronounced decrease in QoL scores was observed in the patients with hemorrhagic brain lesions and visual sequelae of poisoning with abnormal RNFL thickness.

Analysis of fomepizole safety based on a 16-year post-marketing experience in France.

Introduction: Fomepizole has been recommended as first-line antidote to treat ethylene glycol and methanol poisoning. Despite more than 30 years of utilization, the safety of fomepizole when used clinically has not been well documented. Based on the long-standing clinical experience with fomepizole in France, we investigated its safety profile in patients treated for suspected toxic alcohol poisoning.Methods: We designed a 16-year post-marketing study to evaluate the indications for fomepizole prescriptions and to investigate its safety. Data were retrospectively collected using a standardized questionnaire sent each month by post to each French hospital that ordered fomepizole during the month before. The response rate to our survey was 59%.Results: Five hundred and thirty-six patients [188 females/348 males; age, 46 years [34-55] (median [25th-75th percentiles])] were treated with fomepizole [cumulative dose, 18.6 mg/kg [15.5-26.3] (1,268 mg [900-2,100])]. Ethylene glycol/methanol poisoning was confirmed in 275 patients (51%) while a nontoxic exposure was diagnosed in 147 patients (27%). Toxic alcohol poisoning was misdiagnosed in the remaining 114 patients (21%), before the assessment of an alternative poisoning or non-poisoning diagnosis. Fifty adverse reactions were attributed to fomepizole in 36 patients (7%) including general reactions (N = 22), local reactions (N = 22) and laboratory test impairments (N = 6). All were considered mild and transient. None required stopping fomepizole. The most frequent adverse effects were injection site pain/burning (N = 13), nausea/vomiting (N = 8), vessel puncture site inflammation (N = 7), drowsiness/confusion (N = 5) and serum aminotransferase elevation (N = 3). None of the fatalities (N = 37, 7%) or persistent symptoms on discharge (N = 9; 2%) was related to fomepizole.Conclusion: Our longitudinal cohort study supports the safety of fomepizole administered to treat presumed EG and methanol poisoning.

Early dialysis in a rare case of combined toxic alcohols ingestion.

Ingestion of toxic alcohols (TA) typically presents with a high anion gap (AG) metabolic acidosis, and elevated osmolar gap (OG). Hemodialysis (HD) has not been recommended in early phases of intoxication with high OG and normal AG metabolic acidosis. We describe the case of a 40-year-old male who was brought to our emergency department for reported paint thinner ingestion. He was unable to protect his airway and required intubation. Blood gas showed respiratory acidosis, an initial AG, corrected by albumin of 12.75, lactic acid 5.26 mmol/L, and an OG of 170. Patient was treated with bicarbonate drip, fomepizole and emergent HD, which improved his neurologic status. Days after his admission, alcohol levels came positive for a co-ingestion of ethylene glycol, diethylene glycol, and methanol. Most of the TA are metabolized into their toxic byproducts by the enzyme alcohol dehydrogenase (ADH). The kinetics of these alcohols will be altered when there is co-ingestion of multiple substances. Moreover, early ingestions will translate in a high OG without a high AG. False elevation of lactate can occur with the ingestion of ethylene glycol due to a cross-reaction with L-lactate oxidase in the analyzer. In our case, the administration of fomepizole followed by an early HD given the poor clinical improvement, was followed by a fast recovery of the neurological status and potentially prevented renal failure. A high index of suspicion for TA ingestion should be raised when encountering an individual with lactic acidosis, high OG, and normal AG.

The Effect of 4-Methylpyrazole on Oxidative Metabolism of Acetaminophen in Human Volunteers.

INTRODUCTION: Acetaminophen (APAP) is commonly ingested in both accidental and suicidal overdose. Oxidative metabolism by cytochrome P450 2E1 (CYP2E1) produces the hepatotoxic metabolite, N-acetyl-p-benzoquinone imine. CYP2E1 inhibition using 4-methylpyrazole (4-MP) has been shown to prevent APAP-induced liver injury in mice and human hepatocytes. This study was conducted to assess the effect of 4-MP on APAP metabolism in humans. METHODS: This crossover trial examined the ability of 4-MP to inhibit CYP2E1 metabolism of APAP in five human volunteers. Participants received a single oral dose of APAP 80 mg/kg, both with and without intravenous 4-MP, after which urinary and plasma oxidative APAP metabolites were measured. The primary outcome was the fraction of ingested APAP excreted as total oxidative metabolites (APAP-CYS, APAP-NAC, APAP-GSH). RESULTS: Compared with APAP alone, co-treatment with 4-MP decreased the percentage of ingested APAP recovered as oxidative metabolites in 24-hour urine from 4.48 to 0.51% (95% CI = 2.31-5.63%, p = 0.003). Plasma concentrations of these oxidative metabolites also decreased. CONCLUSIONS: These results show 4-MP effectively reduced oxidative metabolism of APAP in human volunteers ingesting a supratherapeutic APAP dose. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03878693.

Fomepizole to treat disulfiram-ethanol reaction: a case series.

Introduction: Disulfiram-ethanol reaction (DER) due to acetaldehyde accumulation occurs after drinking ethanol during disulfiram therapy. DER may result in life-threatening toxicity requiring urgent critical care. Fomepizole, an alcohol dehydrogenase inhibitor used to treat toxic alcohol poisoning, has been suggested for treating DER by preventing the metabolism of ethanol to acetaldehyde. However, its effectiveness and safety have been poorly assessed in this setting.Cases: Ten DER patients (median age, 40 years; 7 males/3 females) were included in the study. DER features consisted of consciousness impairment (median Glasgow coma score, 13; need for mechanical ventilation, 30%) with flushing (50%), vomiting (40%), electrocardiogram abnormalities (30%) and circulatory failure requiring norepinephrine (30%). Patients were successfully treated with a single intravenous infusion of fomepizole (median dose, 7.5 mg/kg). The three patients receiving norepinephrine did not improve until fomepizole was administered. The other seven patients improved promptly following fomepizole infusion without requirement for vasopressor support. All patients fully recovered. Local pain at the injection site was the only reported adverse reaction in one patient.Conclusion: Our case series supports the effectiveness and safety of fomepizole in rapidly reversing DER-induced vasodilatation and toxicity.

Fomepizole as an Adjunctive Treatment in Severe Acetaminophen Toxicity.

A 33-year-old male presented to the emergency department with a chief complaint of abdominal pain after taking #50 500 mg acetaminophen tablets over the preceding two days. He was tachycardic and tachypneic, and the initial labs were notable for acetaminophen level, 337 mg/L; AST, 137 IU/L; ALT, 194 IU/L; ABG pH, 7.24; and lactate, 4.1 mmol/L. The patient was started on IV N-Acetylcysteine (NAC) as well as given a single dose of 15 mg/kg fomepizole. The patient did remarkably well, with a peak AST of 198 IU/L, peak ALT of 301 IU/L, and peak INR of 3.1. Biochemical and animal data support fomepizole having hepatoprotective effects in acetaminophen poisoning. To our knowledge, this is the first human case of an intentional dual NAC/fomepizole regimen for severe acetaminophen toxicity.

Prediction of Human Pharmacokinetics of Fomepizole from Preclinical Species Pharmacokinetics Based on Normalizing Time Course Profiles.

Fomepizole is used as an antidote to treat methanol poisoning due to its selectivity towards alcohol dehydrogenase. In the present study, the goal is to develop a method to predict the fomepizole human plasma concentration versus time profile based on the preclinical pharmacokinetics using the assumption of superimposability on simulated time course profiles of animals and humans. Standard allometric equations with/without correction factors were also assimilated in the prediction. The volume of distribution at steady state (Vss) predicted by simple allometry (57.55 L) was very close to the reported value (42.17 L). However, clearance (CL) prediction by simple allometry was at least 3-fold higher to the reported value (33.86 mL/min); hence, multiple correction factors were used to predict the clearance. Both brain weight and maximum life span potential could predict the CL with 1.22- and 1.01-fold difference. Specifically, the predicted Vss and CL values via interspecies scaling were used in the prediction of series of human intravenous pharmacokinetic parameters, while the simulation of human oral profile was done by the use of absorption rate constant (Ka) from dog following the applicability of human bioavailability value scaled from dog data. In summary, the findings indicate that the utility of diverse allometry approaches to derive the human pharmacokinetics of fomepizole after intravenous/oral dosing.

Delayed Treatment With 4-Methylpyrazole Protects Against Acetaminophen Hepatotoxicity in Mice by Inhibition of c-Jun n-Terminal Kinase.

Acetaminophen (APAP) overdose is the most common cause of hepatotoxicity and acute liver failure in the United States and many western countries. However, the only clinically approved antidote, N-acetylcysteine, has a limited therapeutic window. 4-Methylpyrazole (4MP) is an antidote for methanol and ethylene glycol poisoning, and we have recently shown that cotreatment of 4MP with APAP effectively prevents toxicity by inhibiting Cyp2E1. To evaluate if 4MP can be used therapeutically, C57BL/6J mice were treated with 300 mg/kg APAP followed by 50 mg/kg 4MP 90 min later (after the metabolism phase). In these experiments, 4MP significantly attenuated liver injury at 3, 6, and 24 h after APAP as shown by 80%-90% reduction in plasma alanine aminotransferase activities and reduced areas of necrosis. 4MP prevented c-Jun c-Jun N-terminal kinase (JNK) activation and its mitochondrial translocation, and reduced mitochondrial oxidant stress and nuclear DNA fragmentation. 4MP also prevented JNK activation in other liver injury models. Molecular docking experiments showed that 4MP can bind to the ATP binding site of JNK. These data suggest that treatment with 4MP after the metabolism phase effectively prevents APAP-induced liver injury in the clinically relevant mouse model in vivo mainly through the inhibition of JNK activation. 4MP, a drug approved for human use, is as effective as N-acetylcysteine or can be even more effective in cases of severe overdoses with prolonged metabolism (600 mg/kg). 4MP acts on alternative therapeutic targets and thus may be a novel approach to treatment of APAP overdose in patients that complements N-acetylcysteine.

Butanediol Conversion to Gamma-Hydroxybutyrate Markedly Reduced by the Alcohol Dehydrogenase Blocker Fomepizole.

1,4-Butanediol (BDO)-used as solvent and abused for its euphoric effects-is converted to gamma-hydroxybutyrate (GHB) by the enzyme alcohol dehydrogenase. This double-blind, placebo-controlled crossover study with six healthy volunteers is the first to date investigating the role of the ADH inhibitor fomepizole (4-methylpyrazole (4MP)) in moderating this conversion in humans. Participants received on two different days either intravenous placebo or 15 mg/kg 4MP followed by oral administration of 25 mg/kg BDO. Pretreatment with 4MP resulted in significantly higher BDO maximal plasma concentration (P = 0.001) and area under the concentration-time curve (AUC; P = 0.028), confirming that ADH is the primary pathway for the conversion of BDO to GHB in humans. With 4MP, the mean arterial pressure was significantly lower at 105 minutes compared to baseline (P = 0.003), indicating that blood pressure lowering, observed not with a temporal relationship to 4MP administration but after the maximum BDO concentration was reached, may be an intrinsic effect of BDO.